MTECH Laboratories (Ballston Spa, N.Y.) has developed a number of prototype cryogenic power unidirectional converters for the military. The converters were operated at liquid nitrogen temperature targeting second-generation HTS superconductors and devices. These converter programs have led to several key innovations and advances, such as the development of novel switching topologies, high-speed power busses and cryogenic multi-chip modules to optimize commercially available power devices for low-temperature operation. MTECH's cryogenic power technologies should lead to innovative lightweight, small, and highly efficient bi-directional converters.
For low temperature operation, MTECH has utilized cryogenic MOSFETs, MTECH having more than 30 man-years of combined practical experience in working them into functional devices. The reason cryogenic MOSFETs are preferred is the dramatic reduction in on-state resistance and switching times at low temperatures. MTECH has qualified a select number of commercially available MOSFETs as “cryogenic MOSFETs” and offers them commercially through its subsidiary Cryocircuits, LLC. The performance of one such device is illustrated in FIG. 2, which shows the performance of a cryo-MOSFET, namely, on-resistance, as a function of drain current; and shows a nearly 40-times improvement between 400 K and 77 K at low currents. (Note also that this 28 ampere device can be operated to currents up to 165 amperes at 77 K, with only a minimal increase in on-state resistance.)
MTECH found that there is an optimal balance between size/weight and losses/efficiency, as shown in the optimization curve of FIG. 1. FIG. 1 is a graph illustrating optimization of cryogenic power systems, a tradeoff between electronic component size and refrigerator size.